Mass Migration of Spiny Lobster, Panulirus argus (Crustacea: Palinuridae): Synopsis and Orientation

Abstract

Field and laboratory studies of the autumnal mass migration of the spiny lobster, Pallulims argus, were conducted during the autumns of 1969, 1971-74 at Bimini, Bahamas. We investigated the origin of local migrants, seasonal, and migratory activity patterns, and stimuli triggering the mass migration. Spiny lobsters inhabiting the shallow Bahama bank and deeper reefs surrounding Bimini were diver-monitored before and during the autumnal mass migration. Population characteristics including size-frequency distribution, sex ratios, reproductive state, and molting condition, as well as movements of ultrasonically tagged lobsters, indicated that the majority of migrants originated on the shallow area east of Bimini, with some participation by lobsters from deeper reef populations along the Gulf Stream edge. The net movement of lobsters was westward during the 2-3 week migratory movements. Autumnal storms occurred predictably in the migratory period, and were associated with the mass migration over a period of 10 years. The storm-induced decline in water temperature is circumstantially implicated as a triggering stimulus. The hypothesis that a sharp drop in temperature serves as the environmental trigger for the mass migration was substantiated both in semi-field (natural photoperiod and ambient temperature) and laboratory (both ambient and controlled temperature) studies. Actographs and time-lapse photographic records of lobster groups showed that all three major characteristics of the mass migration (i.e., hyperactivity extending into daylight, continuous queuing, and oriented locomotion) occurred in laboratory pools in association with temperature declines. Water temperature decreases apparently served as a sufficient (if not exclusive) trigger for mass migratory behavior. Visual and time-lapse photographic analysis indicated that the most active lobsters most frequently initiated and became queue leaders.